feat(nodes): traffic-writer queue, full-mirror sync, WS event fixes

- Traffic-writer single-consumer queue (web/service/traffic_writer.go)
  serialises every DB write that touches up/down/all_time/last_online
  (AddTraffic, SetRemoteTraffic, Reset*, UpdateClientTrafficByEmail) so
  overlapping goroutines can no longer clobber each other's column-scoped
  Updates with a stale tx.Save.

- DB pool: WAL + busy_timeout=10s + synchronous=NORMAL + _txlock=
  immediate, MaxOpenConns=8 / MaxIdleConns=4. The immediate-tx PRAGMA
  fixes residual "database is locked [0ms]" cases where deferred-tx
  writer-upgrade conflicts bypass busy_timeout.

- SetRemoteTraffic full-mirrors node-authoritative state into central:
  settings JSON, remark, listen, port, total, expiry, all_time, enable,
  plus per-client total/expiry/reset/all_time. Inbounds and
  client_traffics rows present on node but missing from central are
  created; rows missing from snap are deleted (with cascading
  client_traffics removal).

- NodeTrafficSyncJob detects structural changes from the mirror and
  broadcasts invalidate(inbounds) so open central UIs re-fetch via REST
  on node-side add/del/edit without manual refresh.

- XrayTrafficJob broadcasts invalidate(inbounds) when auto-disable flips
  client_traffics.enable so the per-client toggle reflects depletion
  without manual refresh.

- Frontend: inbounds page now subscribes to the BroadcastInbounds 'inbounds'
  WS event (full-list pushes from add/del/update controllers were silently
  dropped). Fixes invalidate payload field (dataType -> type). Restart-
  panel modal switched from Promise-wrap to onOk-only so Cancel actually
  cancels.

- Node files trimmed of stale prose-comments; cron cadence dropped
  10s -> 5s to match the inbounds page UX.

- README badges and Go module path bumped v2 -> v3 to match module rename.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/composables/useWebSocket.js

@@ -24,7 +24,7 @@ function getSharedClient() {
 //   useWebSocket({
 //     traffic: (payload) => applyTrafficEvent(payload),
 //     client_stats: (payload) => applyClientStatsEvent(payload),
-//     invalidate: ({ dataType }) => { if (dataType === 'inbounds') refresh(); },
+//     invalidate: ({ type }) => { if (type === 'inbounds') refresh(); },
 //   });
 //
 // Built-in lifecycle events ('connected' / 'disconnected' / 'error')